Overview: The current emphasis on fuel economy in the design of power plants for automotive application motivates the efforts to improve the performance of internal combustion engines (ICE) with relatively small displacement. It is well known that automotive vehicles with small displacement engines enjoy moderate fuel usage. However, under high torque conditions such as acceleration and grade ascent, small displacement ICE's often fail to provide satisfactory power. Yet, the conditions demanding high torque generally represent only about one tenth of a vehicle operating time.
Means for improving the performance of automotive vehicles powered by ICE include 1) engine supercharging and 2) a hybrid drive. Supercharging is a method of introducing air for combustion into combustion chambers of an ICE at a pressure in excess of that which can be obtained by natural aspiration (see, for example, McGraw-Hill Dictionary of Scientific and Technical Terms, 6th edition, published by McGraw-Hill Companies Inc., New York, N.Y., 2003). Supercharging is accomplished with a supercharger, which is an air pump, blower or a compressor in the intake system of an ICE used to increase the weight of air charge and consequent power output from a given size engine (see, for example, the above noted McGraw-Hill Dictionary).
A hybrid drive automotive vehicle has a dual propulsion means; one driven directly by the ICE and a second one driven by a battery operated electric motor. During low torque conditions (e.g., constant speed travel on level road), the ICE has a spare power capacity that is used to operate an electric generator and store the produced electric energy in a battery. During high-torque conditions (e.g., acceleration and/or grade ascent), electric energy is extracted from the battery to power the electric motor which assists the ICE in propelling the vehicle.
Superchargers: Supercharges have long been utilized for boosting the power output of ICE's of each spark ignition and compression ignition (diesel). Superchargers can be generally classified according to their source of motive power as engine-driven and exhaust turbine-driven. The latter are also know as turbochargers. A variety of engine-driven superchargers have been developed since the early 1900's. Engine-driven superchargers with nonpositive displacement compressors (i.e., turbine-type) were developed (as disclosed, for example, by Hall-Brown in U.S. Pat. No. 1,645,178) but did not provide adequate flow at low engine speeds associated with high torque conditions. Modern engine-driven supercharger is a positive displacement pump mechanically coupled to the engine usually by means of an on/off clutch. The clutch engages the supercharger when increased engine output is desired and disengages it to reduce engine load when high ICE output is not required. Compression in a supercharger heats up the intake air, thereby reducing its density and adversely impacting ICE performance. This condition is frequently remedied by cooling the output air of a supercharger in a heat exchanger commonly known as an intercooler prior to delivery to ICE intake passage. FIG. 1 shows a typical arrangement of an ICE with an engine-driven supercharger with an intercooler supplying compressed intake air into an intake passage leading to an ICE combustion chamber.
The types of positive displacement pumps used in engine-driven superchargers include a vane pumps (as disclosed, for example, by Casey et al., in U.S. Pat. No. 4,350,135), roots blowers (as disclosed, for example, by Fielden in U.S. Pat. No. 2,067,757), and screw compressors (as disclosed, for example, by Prior in U.S. Pat. No. 6,029,637). These pumps are expensive since they use precision machined and accurately aligned rotor components. Pump rotors spin at high speeds, typically in the range of 5,000 to 20,000 revolutions per minute (rpm), which leads to vibrations and wear. Abrasion and wear gradually increase the precision clearances between mating rotor components which results in reduced supercharger performance. Mitigation of this problem inspired the development of a variety of coatings aimed at reducing the consequences of rotor component wear as disclosed, for example, by Suman et al., in U.S. Pat. No. 6,688,867.
Another limitation of engine-driven superchargers is the low volumetric output at low engine speeds. This can be remedied by a variable speed drive, but only at a significant increase in complexity and cost. Engine-driven superchargers also occupy a relatively large volume which complicates their integration into engine frame. In contrast to early engine-driven superchargers that were external to the engine (as disclosed, for example, by Fielden in U.S. Pat. No. 2,067,757), modern engine-driven superchargers are typically integrated directly into the engine frame (as disclosed, for example, by Kageyama et al. in U.S. Pat. No. 6,453,890). While being more space efficient, integral supercharger obstructs other ICE components and impedes ICE serviceability. Engine-driven supercharger requires significant ICE power to operate and this power must be supplied at the least opportune moment, namely during high demand on ICE output, thus reducing ICE output power available for propulsion. Finally, an engine-driven supercharger must be engaged in a controlled manner to avoid a sudden surge in ICE intake pressure and the consequential sudden surge in output torque. This often requires a complex control system.
Another common supercharger arrangement currently in use is the turbocharger shown in FIG. 2. In a turbocharger, the ICE exhaust flow is utilized to drive an exhaust turbine, which in turn drives a compressor turbine to provide compressed air flow to the engine intake passage. Turbochargers provide the advantages of relatively smooth transitions from natural aspiration to supercharged operation while utilizing residual energy of hot exhaust gas, which would otherwise be largely wasted. However, turbochargers must run at very high rotational speeds (typically on the order of 20,000 to 100,000 rpm) and use sophisticated engineered materials to withstand the high temperatures of ICE exhaust, both of which requires rather costly construction. Another disadvantage of turbochargers is a relatively long response time lag cased by the turbine inertia. Furthermore, the nature of the exhaust gas flow and the turbine drive arrangement causes the supercharging flow to increase exponentially with engine rpm. This results in relatively inadequate boost pressures at low engine speeds and excessive boost pressures at relatively high engine speed. The latter is usually mitigated by control arrangements for reducing or limiting the output flow (e.g., using flow bypassing), but it results in a more complex design.
Ejector Pumps: Ejector pumps are widely used in industry for pumping liquids and gases, see for example, R. H. Perry and C. H. Chilton, “Chemical Engineer's Handbook,” 5th edition, Chapter 6, Section “Ejectors,” pages 6–29 to 6–32, published by McGraw-Hill Book Company, New York, N.Y., 1973, and G. L. Weissler and R. W. Carlson (editors), “Vacuum Physics and Technology,” Chapter 4.3.5: Ejectors, pages 136 to 138, published by Academic Press, New York, N.Y., 1979. One key advantage of ejector pumps is that they have no pistons, rotors, or other moving components. FIG. 3 shows a general configuration of a gas (or steam) operated ejector pump for pumping gases. In this disclosure, the term “ejector pump” shall mean a gas-operated ejector pump. Ejector pump essentially consists of a gas-operated driving nozzle, a suction chamber and a diffuser duct. The diffuser duct typically has two sections; a mixing section which may have converging and/or straight segments, and a pressure recovery section which is usually diverging. The driving nozzle is fed a high-pressure “driving” gas (or steam) at pressure p1 and converts its potential (pressure) energy into a kinetic energy thereby producing a high-velocity gas jet discharging into the suction chamber. Pumping action occurs when the gas in the suction chamber is entrained by the jet, acquires some of its velocity, and is carried into the diffuser duct where the kinetic energy of the mixture of driving and entrained gases is converted into a potential (pressure) energy. In particular, the velocity of the gas mixture is recovered inside the diffuser to a pressure p3 which is greater than the suction pressure p2 but lower than the driving pressure p1. For stable operation the diffuser exit pressure p3 must be equal or higher than the backing pressure p4. Ejector design is termed subsonic if the fluid velocity in the diffuser is subsonic. Conversely, ejector design is termed supersonic if the fluid velocity in the diffuser is supersonic. Typically, diffuser ducts used in ejector pumps have a circular cross-section because it provides the largest cross-sectional area with the least circumference and, therefore, the least wall friction losses.
Ejector pumps can produce compression ratio p3/p2 of up to about 10. To achieve high compression ratio p3/p2 it is necessary that the driving gas pressure p1 is much higher than the target pressure p3 at the exit of the ejector, i.e., p1>>p3. Consequently, ejector pumps can be used as vacuum pumps or as compressors. A supersonic driving nozzle is preferably used to obtain efficient conversion of potential (pressure) energy of the driving gas into kinetic energy of the jet. Ejector pumps can be designed to accommodate a wide variety of flow conditions. As a results, ejector pumps for different applications can greatly vary in size, nozzle and duct shape, and arrangement of components. Data on commercially produced gas ejector pumps and their performance can be found, for example, in “Pumping Gases, Jet Pump Technical Data,” Section 1000, Bulletin 1300, Issued March 1976 by Penberthy Division of Houdaille Industries, Inc., Prophetstown, Ill.
In a fixed ejector design, flow throughput and pressure of driving gas can be varied to produce desired discharge port pressure p3 over a broad range of pumped gas inflows and pressures p2. To increase ejector pump throughput beyond the capacity of a single ejector, several ejector pumps can be operated in parallel. Alternately, multiple driving nozzles can be used to feed a single large cross-section diffuser duct, (see, for example FIGS. 6–71 in the above noted Perry and Chilton).
Use of Ejector Pumps in ICE: The use of ejector pumps in ICE air intake systems and exhaust systems has been disclosed in prior art. In particular, Ikeda et al. in U.S. Pat. No. 6,796,772 and U.S. Pat. No. 6,625,981 discloses ejector pumps driven by ICE intake air flow to generate vacuum for automotive braking system. However, these ejectors do not pump ICE intake air, do not increase the ICE intake air pressure, and do not supercharge the ICE.
Feucht in U.S. Pat. No. 6,267,106, Lundqvist in U.S. Pat. No. 6,502,397, Melchior in U.S. Pat. No. 3,996,748, Radovanovic et al., in U.S. Pat. No. 5,611,204, Gobert in U.S. Pat. No. 5,425,239 and Blake in U.S. Pat. No. 5,974,802 each disclose a fluid pump referred to as an “induction venturi,” “venturi,” and/or “ejector” driven by ICE intake air flow to pump exhaust ICE exhaust gases in an Exhaust Gas Recirculation (EGR) system. In all of these devices the driver gas is the intake air which flows at subsonic speeds. Therefore, the resulting compression ratio is very low albeit sufficient for EGR purposes. Furthermore, these fluid pumps do not increase the ICE intake air pressure and do not supercharge the ICE. Henderson et al. in U.S. Pat. No. 5,611,203 discloses a “multi-lobed” ejector pump operated by compressed air for pumping ERG gases into ICE air intake. This ejector pump does not increase ICE intake air pressure and does not supercharge the ICE.
Henrikson in U.S. Pat. No. 3,257,996 and Sheaffer in U.S. Pat. No. 4,461,251 each discloses an exhaust gas operated “jet pump” for inducing atmospheric air into ICE combustion chamber. These jet pumps have subsonic or sonic driving nozzles operated by puffs of hot exhaust gas generally at near ambient pressure. As a result these jet pumps are inefficient, have a low compression ratio and deliver a warm charge to ICE combustion chamber. In addition, the driver fluid (exhaust gas) becomes ingested in the engine. Increasing the throughput of such jet pump requires increasing the quantity of ingested exhaust gas, which ultimately leads to increased charge temperature and limits the ICE output. Momose et al. in U.S. Pat. No. 4,418,532 discloses a high-pressure air-operated ejector for pumping ICE exhaust gases. This ejector pump does not increase ICE intake air pressure and does not supercharge the ICE. Neuland in U.S. Pat. No. 2,297,910 and McWhorter in U.S. Pat. No. 5,9765,035 each discloses a subsonic ejector-like device operated by ICE exhaust gas, which is used to create a partial vacuum for inducing air into ICE combustion chamber. Since vacuum suction rather than compression is used, this device delivers engine charge at a pressure significantly lower than ambient air pressure. In addition, an exhaust gas driven ejector pump represents an impedance to exhaust gas flow and increases the pumping work done by the ICE.
Use of Compressed Air in ICE Combustion Chambers: Schier et al. in U.S. Pat. No. 4,538,584 discloses a diesel ICE wherein compressed air is fed from a tank into ICE cylinders for the purpose of engine starting. However, compressed air is not used for supercharging during normal ICE operation. Moyer in U.S. Pat. No. 5,529,549 discloses an ICE where engine cylinders are used to compress atmospheric air for storage in a tank and later use for engine supercharging. In Moyer's concept, all of the ICE intake air during supercharging is supplied from the storage tank. This means that the storage tank must have a large storage capacity, which translates to either a large volume or a high tank pressure, neither of which is desirable in an automotive vehicle. In addition, much of the potential (pressure) energy available in compressed air is wasted since the compressed air pressure is be reduced to near ambient intake pressure without performing any useful work. Moreover, Moyer does not show how the air storage tank could be replenished by a compressor driven either by the ICE or an electric motor. Furthermore, no ejector pump is disclosed.
In summary, the prior art does not teach an ICE supercharging system that is effective at the conditions of high torque and low engine speed, has a fast response, is simple, economical, can be retrofitted onto existing ICE, does not dilute engine charge with exhaust gases, and does not rob engine of power during high power demand. Furthermore, the prior art does not teach an ICE supercharged by an ejector pump driven by high-pressure air. In addition, the prior art does not teach an ICE supercharged by an ejector pump with a supersonic driving nozzle.